Body composition and specifically percent body fat detection is relevant in a number of different contexts. For the individual, it can be used as a predictor of cardiovascular disease. In studies, it is useful to characterize and determine the mechanisms of sarcopenia, defined as the muscle loss with age, and other catabolic conditions. For example, in populations undergoing drug therapy to stall or reverse the effects of wasting diseases such as AIDS, body composition assessment can be used to quantify the efficacy of those drugs.
A number of techniques exist for detecting percent body fat in animals. Hydrodensitometry, bioelectrical impedance analysis (BIA), and dual energy absorptiometry (DXA) are examples based upon the influence of body fat or hydration on physical properties of the body, such as density, electrical impedance, and photon attenuation properties. Other techniques for single compartment body composition analysis are available, some of which are correlated to percent body fat. Body water can be measured by isotope dilution using D.sub.2 O, .sup.3 H.sub.2 O or H.sub.2.sup.18 O. Body protein is measured by direct measurement of total body nitrogen (TBN) using prompt-gamma neutron activation. Body cell mass, a compartment overlapping with both water and protein, is measured by gamma counting of the natural radioactivity of the body's .sup.40 K.